As Internet of Things (IoT) is more and more widely used in the next generation of mobile communication networks, new wireless communication technology for supporting IoT business, i.e., a subject of a technology of narrow band Internet of Things (NB-IoT), is under study in the 3rd generation partnership project (3GPP).
IoT business has many new features, including ultra-low power consumption requirement, deployment of massive user equipment (UE), relatively less flow of data, and relatively low requirement on traffic latency, etc. Such features pose many technical requirements to an LTE system, in which the most important requirement includes the ultra-low power consumption requirement on the user equipment.
The NB-IoT technology is a new narrow band communication technology based on the existing LTE technology and enhanced to satisfy IoT business demands. In an NB-IoT random access procedure, a user equipment (UE) selects a time-frequency resource used for transmitting a preamble according to configuration of the network, and calculates a random access radio network temporary identity (RA-RNTI) according to the selected resource. The network side obtains the RA-RNTI used by the UE according to a position of the resource for transmitting the preamble by the UE, and transmits a random access response (RAR) scrambled by the RA-RNTI to the UE. The UE descrambles a physical downlink control channel (PDCCH) by using the RA-RNTI, and further decodes an RAR corresponding to the UE.
In an LTE system, RA-RNTI=1+t_id+10*f_id; where, t_id denotes a subframe number selected by the UE for transmitting a preamble, and f_id denotes a position of a frequency resource selected by the UE for transmitting the preamble. RARs of multiple UEs may be multiplexed into a protocol data unit (PDU) of a media access control (MAC) layer for transmission. Multiple RARs in one MAC PDU are differentiated by sequence numbers of preambles.
In an NB-IoT system, sequence numbers of preambles used by all UEs are identical, and a random access opportunity for transmitting the preambles appears once at most 40 ms. Hence, t_id is not embodied any longer in the calculation of the RA-RNTI, while a system frame number (SFN) is used to denote a time-domain position for transmitting a preamble by the UE. And f_id is used to differentiate different RARs multiplexed in one MAC PDU. Hence, RA-RNTI=1+(SFN/4).
It should be noted that the above description of the background is merely provided for clear and complete explanation of this disclosure and for easy understanding by those skilled in the art. And it should not be understood that the above technical solution is known to those skilled in the art as it is described in the background of this disclosure.